Cement oil-based mud spacer formulation

ABSTRACT

A spacer fluid made of a viscosity thinner, a weighting agent, an antifoaming agent, and a non-ionic surfactant in a base aqueous fluid is disclosed. In some instances, the viscosity thinner is a sulfomethylated tannin, the weighting agent is barium sulfate, the antifoaming agent is a silicone, and the non-ionic surfactant is an ethoxylated alcohol. A method of treating a well bore annulus in preparation of introducing water-based cement slurry into a well bore using the spacer fluid is disclosed. A method of using the spacer fluid to position a first fluid into a well bore annulus of a well bore containing a second fluid is disclosed. A method for fluidly isolating at least a portion of a well bore annulus in a well bore containing an oil-based drilling fluid using water-based cement slurry and the spacer fluid is disclosed.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional of U.S. Non-Provisional applicationSer. No. 13/650,451, filed on Oct. 12, 2012, which claims priority toand the benefit of U.S. Provisional Application No. 61/546,317, filedOct. 12, 2011. For purposes of United States patent practice, thisapplication incorporates the contents of the Provisional Application andParent Application by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of invention relates to a spacer fluid composition and methodof use. More specifically, the field relates to a composition and methodof using a spacer fluid that is compatible with both oil-based fluidsand water-based fluids simultaneously.

2. Description of the Related Art

Well Bore, Tubular and Fluid Conduit

A well bore is a hole that extends from the surface to a location belowthe surface. The well bore can permit access as a pathway between thesurface and a hydrocarbon-bearing formation. The well bore, defined andbound along its operative length by a well bore wall, extends from aproximate end at the surface, through the subsurface, and into thehydrocarbon-bearing formation, where it terminates at a distal well boreface. The well bore forms a pathway capable of permitting both fluid andapparatus to traverse between the surface and the hydrocarbon-bearingformation.

Besides defining the void volume of the well bore, the well bore wallalso acts as the interface through which fluid can transition betweenthe interior of the well bore and the formations through which the wellbore traverses. The well bore wall can be unlined (that is, bare rock orformation) to permit such interaction with the formation or lined (thatis, with casing, tubing, production liner or cement) so as to not permitsuch interactions.

The well bore usually contains at least a portion of at least one fluidconduit that links the interior of the well bore to the surface.Examples of such fluid conduits include casing, liners, pipes, tubes,coiled tubing and mechanical structures with interior voids. A fluidconduit connected to the surface is capable of permitting regulatedfluid flow and access between equipment on the surface and the interiorof the well bore. Example equipment connected at the surface to thefluid conduit includes pipelines, tanks, pumps, compressors and flares.The fluid conduit is sometimes large enough to permit introduction andremoval of mechanical devices, including tools, drill strings, sensorsand instruments, into and out of the interior of the well bore.

The fluid conduit made from a tubular usually has at least twoopenings—typically on opposing ends—with an enclosing surface having aninterior and exterior surface. The interior surface acts to define thebounds of the fluid conduit. Examples of tubulars and portions oftubulars used in the well bore as fluid conduits or for making orextending fluid conduits include casing, production liners, coiledtubing, pipe segments and pipe strings. An assembly of several smallertubulars connected to one another, such as joined pipe segments orcasing, can form a tubular that acts as a fluid conduit.

When positioning a tubular or a portion of tubular in the well bore, thevolume between the exterior surfaces of the fluid conduit or tubularportion and the well bore wall of the well bore forms and defines a wellbore annulus. The well bore annulus has a volume in between the externalsurface of the tubular or fluid conduit and the well bore wall.

Well Bore Fluid

The well bore contains well bore fluid from the first moment offormation until completion and production. The well bore fluid servesseveral purposes, including well control (hydraulic pressure against thefluids in the hydrocarbon-bearing formation), well bore wall integrity(hydraulic pressure on the well bore wall; provides loss controladditives) and lubricity (operating machinery). Well bore fluid is influid contact with all portions of and everything in the well bore notfluidly isolated, including the tubular internal fluid conduit, the wellbore annulus and the well bore wall. Other fluid conduits coupled to thewell bore often contain at least some well bore fluid.

While drilling, drilling fluid (“mud”) fills the interior of the wellbore as the well bore fluid. Some muds are petroleum-based materials andsome are water-based materials. Petroleum-based materials comprise atleast 90 weight percent of an oil-based mud (OBM). Examples of suitablebase petroleum materials include crude oils, distilled fractions ofcrude oil, including diesel oil, kerosene and mineral oil, and heavypetroleum refinery liquid residues. A minor part of the OBM is typicallywater or an aqueous solution that resides internally in the continuouspetroleum phase. Other OBM components can include emulsifiers, wettingagents and other additives that give desirable physical properties.

Oil-based muds also include synthetic oil-based muds (SOBMs). Syntheticoil-based muds are crude oil derivatives that have been chemicallytreated, altered or and refined to enhance certain chemical or physicalproperties. In comparison to a crude temperature fraction of apartially-refined crude oil, which may contain several classes (forexample, alkane, aromatic, sulfur-bearing, nitrogen-bearing) ofthousands of individual compounds, a SOBM can comprise one class withonly tens of individual compounds (for example, esters compounds in aC₈₋₁₄ range). Examples of materials used as base fluids for SOBMsinclude linear alpha olefins, isomerized olefins, poly alpha olefins,linear alkyl benzenes and vegetable and hydrocarbon-derived estercompounds. SOBMs are monolithic systems that behave in a manner as ifthey were an oil-based mud but provide a more narrow and predictablerange of chemical and physical behaviors.

While performing drilling operations, well bore fluid circulates betweenthe surface and the well bore interior through fluid conduits. Well borefluid also circulates around the interior of the well bore. Theintroduction of drilling fluid into the well bore through a first fluidconduit at pressure induces the motivation for the fluid flow in thewell bore fluid. Displacing well bore fluid through a second fluidconduit connected to the surface causes well bore fluid circulation fromthe first fluid conduit to the second fluid conduit in the interior ofthe well bore. The expected amount of well bore fluid displaced andreturned to the surface through the second fluid conduit is equivalentto the amount introduced into the well bore through the first fluidconduit. Parts of the well bore that are fluidly isolated do not supportcirculation.

Drilling muds that are not water based tend to dehydrate and loseadditives during drilling operations. Dehydrated and additive-poorresidues can collect in lower-flow velocity parts as solids, gels andhighly viscous fluids. “Filter cake” is a layer of deposited solids andgelled drilling fluid that adheres to the interior surfaces of the wellbore, including the well bore wall and the exterior of the fluidconduit.

Cementing the Well Bore

Cementing is one of the most important operations in both drilling andcompletion of the well bore. Primary cementing occurs at least once tosecure a portion of the fluid conduit between the well bore interior andthe surface to the well bore wall of the well bore.

A variety of water-based cements slurries is available for primarycementing operations. Primary cements typically contain calcium,aluminum, silicon, oxygen, iron and sulfur compounds that react, set andharden upon the addition of water. The water used with the cement slurrycan be fresh water or salt water and depend on the formation of thecement slurry and its tolerance to salts and free ions. Suitablewater-based cements include Portland cements, pozzolana cements, gypsumcements, high alumina content cements, slag cements, silica cements,high alkalinity cements, latex and resin-based cements. Cement slurriesuseful primary cementing operations meet the standards given by theAmerican Petroleum Institute (API) in Specification 10A for classes A-H.

Primary cementing forms a protective solid sheath around the exteriorsurface of the introduced fluid conduit by positioning cement slurry inthe well bore annulus. Upon positioning the fluid conduit in a desirablelocation in the well bore, introducing cement slurry into the well borefills at least a portion if not all of the well bore annulus. When thecement slurry cures, the cement physically and chemically bonds withboth the exterior surface of the fluid conduit and the well bore wall,coupling the two. In addition, the solid cement provides a physicalbarrier that prohibits gases and liquids from migrating from one side ofthe solid cement to the other via the well bore annulus. This fluidisolation does not permit fluid migration uphole of the solid cementthrough the well bore annulus.

Displacing well bore fluid for primary cementing operations is similarto establishing circulation in the well bore fluid with a drilling mud.An amount of cement slurry introduced into the well bore through a firstfluid conduit induces fluid flow in the well bore and displaces anequivalent amount of well bore fluid to the surface through a secondfluid conduit. In such an instance, the well bore fluid includes aportion of the well bore fluid previously contained in the well borebefore cement introduction as well as the amount of the introducedcement slurry.

Cementing in the presence of filter cake can cause a cementing job tofail. The adhesion of filter cake and gelled fluid to the well bore wallor the tubular exterior is weak compared to the bond that cement canmake. Cementing on top of filter cake strips the cake off the walls andexterior surfaces due to the weight of the cement upon curing. This lackof direct adhesion creates fluid gaps in and permits circulation throughthe well bore annulus.

Incompatible Fluid Interaction

Direct contact between the water-based cement slurry and the oil-baseddrilling mud can result in detrimental fluid interactions that canjeopardize not only cementing operations but also the integrity of thewell bore. The intermingling of incompatible fluids can create emulsions(both water-in-oil and oil-in-water emulsions) between the fluids. Theemulsions, which resist fluid movement upon the application of force,raises the viscosity profile of the well bore fluid. Increasing pumpinghead pressure to maintain a constant fluid circulation rate in the wellbore can result in damaging the formation downhole as well bore fluidpressure exceeds the fracture gradient of the formation.

Besides detrimentally affecting the viscosity profile, when solids andwater from the cement slurry transfer into the oil-based drilling mudduring emulsification, the oil-based mud properties are detrimentallyaffected. Dilution, chemical interaction, breaking of a water-in-oilemulsion and flocculation of suspended additives out of the oil phasecan also occur.

Cement slurry properties can also suffer from contamination by the OBM.Flocculation of weighting agents and macromolecules can cause the cementto have reduced compressive strength. The diffusion of ionic speciesfrom the OBM can cause premature setting of the cement slurry. Theramifications of early cement hardening include equipment damage, timedelay, well bore damage and possible loss of the entire tubular string.Contamination of the cement slurry with bulk OBM results in higherslurry viscosity and higher fluid losses from the hardening slurry.

SUMMARY OF THE INVENTION

The invention includes a composition for use as a spacer fluid betweentwo incompatible fluids having a viscosity thinner, a weighting agent,an antifoaming agent and a non-ionic surfactant in a base aqueous fluid.The spacer fluid is compatible with both fluids. An embodiment of thecomposition includes having a composition with a sulfomethylated tanninviscosity thinner, a barium sulfate weighting agent, a siliconeantifoaming agent and an ethoxylated alcohol non-ionic surfactant.

The invention includes a method of treating a well bore annulus inpreparation of introducing water-based cement slurry into a well bore.The well bore contains a well bore fluid. The method includes the stepsof introducing a spacer fluid into the well bore and positioning thespacer fluid in the well bore annulus. The spacer fluid water-wets theexterior surface of the tubular and the well bore wall such that thewater-based cement slurry can adhere to both surfaces. The spacer fluidis made of a chemically modified tannin, barite, a silicone liquid andan ethoxylated alcohol in an aqueous base fluid. The spacer fluid iscompatible with both the water-based cement slurry and the well borefluid. The spacer fluid is operable to separate physically thewater-based cement slurry from the fluid in the well bore.

The invention includes a method of using the spacer fluid to position afirst fluid into a well bore annulus of a well bore containing a secondfluid. The spacer fluid is made of a chemically modified tannin, barite,a silicone liquid and an ethoxylated alcohol in an aqueous base fluid.The method includes the step of introducing into the well bore through afirst fluid conduit an amount of the spacer fluid. The spacer fluidfluidly couples with the second fluid. The spacer fluid introductiondisplaces an equivalent amount of the fluid in the well bore through asecond fluid conduit. The spacer fluid introduction is at a pressureadequate to induce laminar fluid flow of the fluid in the well boreannulus. The method also includes the step of introducing into the wellbore through the first fluid conduit an amount of the first fluid. Thefirst fluid fluidly contacts the spacer fluid in the well bore. Thefirst fluid introduction displaces an equivalent amount of the fluid inthe well bore through the second fluid conduit. The first fluidintroduction induces laminar fluid flow of the fluid in the well boreannulus. The method includes the step of positioning a portion of thefirst fluid in the well bore annulus.

The invention includes a method for fluidly isolating at least a portionof a well bore annulus in a well bore containing an oil-based drillingfluid using water-based cement slurry. The spacer fluid is made of achemically modified tannin, barite, a silicone liquid and an ethoxylatedalcohol in an aqueous base fluid. The water-based cement slurry and theoil-based drilling fluid are incompatible with one another; however,both are compatible with the spacer fluid. The method includes the stepof introducing into the well bore through the first fluid conduit anamount of spacer fluid. The spacer fluid couples to the oil-baseddrilling fluid in the well bore. The spacer fluid introduction displacesan equivalent amount of the fluid in the well bore through the secondfluid conduit. The spacer fluid introduction induces laminar fluidcirculation of the fluid in the well bore through the well bore annulus.The method also includes the step of positioning the spacer fluidcomposition in the well bore annulus such that the spacer fluidcomposition fluidly contacts a portion of the tubular exterior surfaceand a portion of the well bore wall of the well bore annulus. The spacerfluid contacting the surfaces makes both surfaces water-wet. The methodalso includes the step of introducing into the well bore through thefirst fluid conduit an amount of water-based cement slurry. Thewater-based cement slurry contacts the spacer fluid in the well bore.The water-based cement slurry introduction displaces an equivalentamount of the fluid in the well bore through a second fluid conduit. Thewater-based cement slurry introduction induces laminar fluid circulationof the fluid in the well bore through the well bore annulus. Thewater-based cement is operable to cure into solid cement at well boreconditions. The method also includes the step of positioning thewater-based cement slurry such that at least a portion of thewater-based cement slurry fluidly contacts both the external surface ofthe tubular and the well bore wall of the well bore at the same time.The method also includes the step of maintaining the water-based cementslurry in the well bore annulus until the water-based cement slurryadheres to the water-wetted portions of the tubular exterior surface andthe well bore wall. Maintaining the position also occurs until thecement slurry cures into the solid cement material. When the water-basedcement cures into a solid cement material in the well bore annulus, aportion of the well bore annulus is fluidly isolated from the remainderof the well bore.

The spacer fluid composition positioned between the water-based cementslurry and the oil-based drilling mud prevents negative directinteractions between the incompatible fluids. The spacer fluid ischemically compatible with both water-based fluids, including cementslurries, and oil-based fluids, including oil-based drilling fluids ormuds, simultaneously.

Compatible fluids can form a fluid mixture that does not undergoundesirable chemical or physical reactions. An indication of physicalcompatibility between fluids includes determining the rheologicalattributes, including shear viscosity, of the blend of fluids. Chemicalcompatibility includes no or desirable changes to chemical-relatedattributes, including thickening time, compressive strength of resultantsolids, static gels and fluid loss. Verifying compatibility ensures thatthe introduction of the spacer fluid into the well bore does not createnew incompatibilities.

The spacer fluid composition is such that if the spacer fluid iscontaminated by both the water-based fluid and the oil-based fluid inamounts as great as 25 percent by volume of the total fluid volume thatthe contaminated spacer fluid can be circulated without requiringsignificantly higher fluid head pressure than uncontaminated spacerfluid. The spacer fluid does not harden, gelatinize or otherwise becomeimmobile in the well bore because of contamination.

In using the spacer fluid, the two fluids do not have to be incompatiblewith one another. In some situations, the separated fluids may be “toocompatible” with one another mingle. This mingling of like fluids maycause the two fluids to lose their advantageous attributes. The spacerfluid is also useful for separating different drilling fluids duringdrilling fluid change outs, for separating a drilling fluid and anaqueous fluid, including a completion brine or seawater, during wellintegrity testing, and for “water-wetting” the well bore wall andsurfaces in the well bore.

BRIEF DESCRIPTION OF THE DRAWINGS

No drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The Specification, which includes the Summary of Invention, BriefDescription of the Drawings and the Detailed Description of thePreferred Embodiments, and the appended Claims refer to particularfeatures (including process or method steps) of the invention. Those ofskill in the art understand that the invention includes all possiblecombinations and uses of particular features described in theSpecification. Those of skill in the art understand that the inventionis not limited to or by the description of embodiments given in theSpecification. The inventive subject matter is not restricted exceptonly in the spirit of the Specification and appended Claims.

Those of skill in the art also understand that the terminology used fordescribing particular embodiments does not limit the scope or breadth ofthe invention. In interpreting the Specification and appended Claims,all terms should be interpreted in the broadest possible mannerconsistent with the context of each term. All technical and scientificterms used in the Specification and appended Claims have the samemeaning as commonly understood by one of ordinary skill in the art towhich this invention belongs unless defined otherwise.

As used in the Specification and appended Claims, the singular forms“a”, “an”, and “the” include plural references unless the contextclearly indicates otherwise. The verb “comprises” and its conjugatedforms should be interpreted as referring to elements, components orsteps in a non-exclusive manner. The referenced elements, components orsteps may be present, utilized or combined with other elements,components or steps not expressly referenced. The verb “couple” and itsconjugated forms means to complete any type of required junction,including electrical, mechanical or fluid, to form a singular objectfrom two or more previously non-joined objects. If a first devicecouples to a second device, the connection can occur either directly orthrough a common connector.

Spatial terms describe the relative position of an object or a group ofobjects relative to another object or group of objects. The spatialrelationships apply along vertical and horizontal axes. Orientation andrelational words including “up” and “down” and other like terms are fordescriptive convenience and are not limiting unless otherwise indicated.

Where a range of values is provided in the Specification or in theappended Claims, it is understood that the interval encompasses eachintervening value between the upper limit and the lower limit as well asthe upper limit and the lower limit. The invention encompasses andbounds smaller ranges of the interval subject to any specific exclusionprovided.

All publications mentioned in the Specification are incorporated byreference to disclose and describe the methods or materials, or both, inconnection with which the publications are cited.

Where reference is made in the Specification and appended Claims to amethod comprising two or more defined steps, the defined steps can becarried out in any order or simultaneously except where the contextexcludes that possibility.

Spacer Fluid Composition

The spacer fluid includes a base aqueous fluid, a viscosifier, aweighting agent, a non-ionic surfactant and an antifoaming agent. Theviscosifier has a component that can act to thin gels to ease removingthem from well bore walls and surfaces. In addition, the thinnercomponent interacts with charged particles in the well bore fluid tosuspend them for removal from the well bore. The weighting agentincreases the density of the spacer fluid so that it fits in the densityprofile between the fluids it is separating to prevent fluid inversionor fingering. The weighting agent also assists with increasing thebuoyancy effect of the spacer fluid on gelled drilling fluids and filtercake. The non-ionic surfactant enhances the chemical compatibility ofthe spacer fluid with the oil-based fluid. The surfactant leaves boththe well bore wall and exposed surfaces in the well bore interior“water-wet” by removing non-aqueous materials, which enhances thecapability of the cement to adhere to the surfaces. The surfactant alsointeracts with hydrocarbon-coated solids to suspend them in the aqueoussolution for transport out of the well bore. The antifoaming agentprevents the formation of foams and emulsions between the aqueous andhydrocarbon-based fluids by lowering the surface tension between thematerials.

Although not intending to be bound by theory, many of the components ofthe spacer fluid composition can secondarily supplement desirableproperties of the spacer fluid. For example, the antifoaming agent canalso act as a minor surfactant in certain operative environments.

Base Aqueous Fluid

The base aqueous fluid of the spacer fluid composition can includedeionized, tap, distilled or fresh waters; natural, brackish andsaturated salt waters; natural, salt dome, hydrocarbon formationproduced or synthetic brines; filtered or untreated seawaters; mineralwaters; and other potable and non-potable waters containing one or moredissolved salts, minerals or organic materials. Fresh water ispreferable because of potential issues with introducing unnecessaryamounts of ions, metals and minerals to cement slurry compositions thatare more sensitive to such materials. The base aqueous fluid is presentin a range of from about 70% to about 95% of the total volume of thespacer fluid composition.

Viscosifier

The spacer fluid composition includes a viscosifier. The viscosifierinduces rheological properties (that is, thickening) in the spacer fluidcomposition that supports particle suspension and helps to preventlosses into the other fluids or the formation. The viscosifier caninclude biological polymers, clays, ethoxylated alcohols and polyetherglycols. Biological polymers and their derivatives includepolysaccharides, including xanthan gums, welan gums, guar gums,cellulose gums, corn, potato, wheat, maize, rice, cassava, and otherfood starches, succinoglycan, carrageenan, and scleroglucan and otherintracellular, structural and extracellular polysaccharides. Biologicalpolymers also include chemically modified derivatives such ascarboxymethyl cellulose, polyanionic cellulose and hydroxyethylcellulose (HEC) and forms of the polymers suspended in solvents. Claysand their derivatives include bentonite, sepiolite, attapulgite, andmontmorillionite. Polyalklyene glycols include polyethylene glycols andpolypropylene glycols, which are macromolecules with a series ofinternal ether linkages. Polyalklyene glycols are capable of dissolvingin water and have a greater impact on viscosity with higher molecularweight.

The viscosifier can also include a viscosity thinner. A viscositythinner reduces flow resistance and gel development by reducingviscosity of the spacer fluid. Thinners can reduce the flow resistanceand gel development of filter cake and disrupt gelled materials that thespacer fluid composition contacts in the well bore. Thinners comprisinglarge molecular structures can also act as fluid loss additives. Thefunctional groups of the viscosity thinners can act to emulsify oils andhydrocarbons present in the aqueous phase. Chemically modified viscositythinners can attract solids and particles in the spacer fluid anddisperse such particles, the dispersion of particles preventing anyincrease in viscosity of the spacer fluid due to aggregation. Ionicthinners can counter-act the effects of cement slurry intrusion into theaqueous spacer. Cement intrusion in the spacer fluid composition canresult in greater saline concentration or higher pH, which in turn cancause the gel strength or the yield point value, or both, of the spacerfluid to rise. Low gel strength and yield point values are preferred tomaintain lower spacer fluid pumping pressure.

Polyphenolics, which include tannins, lignins, and humic acids, andchemically modified polyphenolics are useful viscosity thinners. Tanninsand their chemically modified derivatives can either originate fromplants or be synthetic. Examples of plant-originating tannins includetannins from pine, redwood, oak, and quebracho trees and bark; grapesand blueberries; and walnuts and chestnuts.

Chemically modified tannins include sulfomethylated and othersulfoalkylated tannins, causticized tannins, sulfited tannins,sodium-complexed tannin and sulfomethylated quebracho. Chemicallymodified lignins include sodium lignosulfonates, sugar-containinglignosulfonates, and de-sugared lignosulfonates. Humic acids, such asthose extracted from decaying tree bark, are also useful rheologymodifiers. Useful polyphenoics dissolve in the base aqueous fluid. Insome instances, the chemically modified tannin pairs with similar ionicspecie to assist in dissolving the tannin in the aqueous solution. Forexample, sulfomethylated tannins paired with ferrous sulfates aresoluble in aqueous solutions.

A commercially available viscosifier useful in an embodiment of thespacer fluid composition includes DIACEL® Adjustable Spacer Viscosifier(Drilling Specialties Co.; The Woodlands, Tex.).

The viscosifier is present in the spacer fluid composition by weight perbarrel of base aqueous solution in the spacer fluid composition. Theviscosifier is present in the spacer fluid composition in a range offrom about 5 pounds to about 10 pounds per barrel of base aqueous fluid.One of ordinary skill in the art recognizes the appropriate amount ofviscosifier for the spacer fluid composition given the applicationcircumstances and therefore understands that all values within theprovided range are included.

Weighting Agent

The spacer fluid composition also contains a weighting agent. Theweighting agent provides the spacer fluid with the proper densityprofile to separate the fluids from one another. The proper weighing ofthe spacer fluid composition relative to each fluid ensures that thespacer fluid composition does not “invert” with one of the other fluidspresent in the well bore. Weighting agents include sand, barite (bariumsulfate), hematite, fly ash, silica sand, ilmenite, manganese oxide,manganese tetraoxide, zinc oxide, zirconium oxide, iron oxide and flyash. The preferred weighting agent for the spacer fluid composition isbarite. Embodiments of the spacer fluid composition include compositionsnot including calcium carbonate as the weighting agent.

The weighing agent is present in the spacer fluid composition by weightper barrel of base aqueous solution in the spacer fluid composition. Theweighting agent is present in the spacer fluid composition in a range offrom about 100 pounds to about 400 pounds per barrel of base aqueousfluid. One of ordinary skill in the art recognizes the appropriateamount of weighing agent for the spacer fluid composition given theapplication circumstances and therefore understands that all valueswithin the provided range are included.

The density profile of the spacer fluid composition relative to theother fluids is such that the spacer fluid composition has a similar orgreater density than the displaced fluid but has a lower density thanthe displacing fluid. In some instances, the displaced fluid is theoil-based mud and the displacing fluid is the water-based cement slurry.The higher density spacer fluid composition pushes gelled and solidremnants of the displaced fluid away from the well bore wall and fluidconduit exteriors.

The spacer fluid composition has a density in the range of from about 70to about 120 pounds per cubic foot. One of ordinary skill in the artrecognizes that spacer fluids can have a density at any value withinthis range given the application circumstances and therefore understandsthat all values within the provided range are included.

Antifoaming Agent

The spacer fluid composition also includes an antifoaming agent.Antifoaming agents reduce surface tension and prevent emulsions fromforming between the aqueous spacer fluid composition and hydrocarbons inthe OBM and in the well bore interior.

An embodiment of the spacer fluid composition includes an antifoamingagent that is a polysiloxane material. Polysiloxanes are macromoleculesthat have branched or unbranched backbones consisting of alternatingsilicon and oxygen atoms with hydrocarbon or hydrogen branching groups.“Silicone” and “silicone oil” are other names for polysiloxanes.Examples of silicones include polydimethylsiloxane (dimethicone; PDMS),polymethylhydrosiloxane (PMHS) and polydiphenylsiloxane (PDPS).Silicones can be end-capped with functional groups such as methyl andhydroxyl groups. The antifoaming agent is a preferably a silicone-basedliquid.

To improve water solubility in aqueous solutions while retaining theability for the silicone to interact with non-aqueous systems, somesilicone antifoams include polysiloxanes copolymerized withpolyoxyalkylene functional groups to form copolymers. Thecopolymerization can be branch or block. Some refer to copolymers ofsilicone and ethoxylated, propoxylated or co-ethoxylated/propoxylatedglycols as “silicone copolyols”, “silicone glycols” and “siliconepolyethers”.

Silicone oils and glycols can combine with treated silica materials toform antifoaming agents. The silica acts to push the silicone fluidthrough the foam and assist it onto the foam surface. Silica can alsoact to disrupt foam formation. Examples of useful treated silica includemethylated silica, trimethylated silica, treated amorphous silica,PDMS-treated silica and amorphous fumed silica.

Crude oil hydrocarbon fraction and compounds from crude oil are alsouseful as antifoaming agents. Examples include paraffinic oils andmineral oils. Vegetable oils, including corn oil, and legume oils,including peanut oil, are also useful antifoaming agents. Fatty alcoholshaving a carbon count in a range from 8 to 32 carbons are also usefulantifoaming agents. Polyoxyalkylene co- and tri-block polymerscontaining propylene oxides or butylene oxides, or both, with ethyleneoxides, can disrupt emulsion combinations.

A commercially available antifoaming agent useful in an embodiment ofthe spacer fluid composition includes DIACEL® ATF-S (DrillingSpecialties Co.; The Woodlands, Tex.).

The antifoaming agent is present in the spacer fluid composition byvolume per barrel of base aqueous solution in the spacer fluidcomposition. The antifoaming agent is present in the spacer fluidcomposition in a range of from about 0.01 gallons to about 0.2 gallonsper barrel of base aqueous fluid. One of ordinary skill in the artrecognizes the appropriate amount of antifoaming agent for the spacerfluid composition given the application circumstances and thereforeunderstands that all values within the provided range are included.

Non-Ionic Surfactant

The spacer fluid composition contains a non-ionic surfactant. Thenon-ionic surfactant is a surface-active agent that does not dissociateinto ions in aqueous solutions, unlike an anionic surfactant, which hasa negative charge, and a cationic surfactant, which has a positivecharge, in an aqueous solution. The non-ionic surfactant is compatiblewith both ionic and non-ionic components of the spacer fluid compositionbecause it is charge-neutral. Hydrophilic functional groups present onnon-ionic surfactants can include alcohols, phenols, ethers, esters andamides. Non-ionic surfactants are widely used as detergents, have goodsolvency in aqueous solutions, exhibit low foam properties and arechemically stable.

An embodiment of the spacer fluid composition includes a non-ionicsurfactant that is an ethoxylated alcohol. Some refer to ethoxylatedalcohols as “polyoxyalkylene glycol alkyl ethers”, which describes thereaction product of an alcohol (alkyl) with the degree of ring-openingoligiomerization that the alkyloxide undergoes to form the ethoxylatedreaction product (polyoxyalkylene glycol). Both sections of theresultant molecule join through an ether link. The non-ionic surfactantin some instances is an ethoxylated alcohol.

Alcohols useful to form the alkyl portion of the ethoxylated alcoholinclude normal, iso-, and cyclo-aliphatic alcohols. Example alcoholsinclude fatty alcohols and long-chained alcohols with slight branchinghaving a carbon count from about 3 to about 30 carbons, isopropanol,n-butanol and cyclohexanol. Primary and secondary alcohols are included.

The degree of ethoxylation for the ethoxylated alcohol depends onseveral factors. The degree of ethoxylation, which refers to the numberof ethylene oxides used to form the polyoxyethylene glycol portion ofthe surfactant, can range from about 2 to about 50 for the ethoxylatedalcohol. Considerations include the carbon count of the alcohol, thedesired overall solubility of the surfactant in the spacer fluid,foaming/emulsion effects of the surfactant-hydrocarbon complex, and thebalance between hydrophobic effects of the alkyl portion of thesurfactant to the hydrophilic effects of the polyethoxylated portion ofthe surfactant. For fatty alcohols, the degree of ethoxylation istypically between about 4 and about 40 depending on the end-use of theethoxylated fatty alcohol.

Other useful non-ionic surfactants for the spacer fluid compositioninclude ethoxylated phenols and ethoxylated alkyl phenols. The etherlink between the ethoxylated portion and the phenol/alkyl phenol portionof the surfactant forms from reaction of the alcohol moiety on thephenol. For alkyl phenols, an alkyl functional group extends from thephenol that contributes to the hydrophobic properties of the surfactant.Example alkyl phenols include dodecylphenols, nonyiphenols,octylphenols. The degree of ethoxylation ranges from about 4 to about50.

Non-ionic surfactants for the spacer fluid composition also includevarious epoxide block co-polymerizations of ethylene oxide with otheralkoxylates, including components formed from propylene oxide andbutylene oxide. The alkoxylates are capable of forming co-, ter-, andhigher order macromolecules and polymers. For example, a polypropyleneoxide glycol (hydrophobic portion) allowed to react with severalethylene oxides can form an ABA configuration EO/PO/EO polymericsurfactant. These alkoxylated tri-block macromolecules are also known as“poloxamers”.

Examples of other useful non-ionic surfactants for the spacer fluidcomposition include fatty alcohols; alkypolyglucosides; alkoxylated oilsand fats, including ethoxylated lanolin, castor oil, and soy bean oil;fatty amine ethoxylates; alkanolamides, including monoalkanolamides,dialkanolamides, and esteramides; alkoxylated alkanolamides, includingpolyethoxylated monoalkanolamides and polyethoxylated dialkanolamide;alkoxylated fatty acid monoesters and diesters; alkoxylated gylcols andglycol esters, including ethoxylated glycol monoester and ethoxylatedglycerol monoester; alkoxylated amines, including mono-, di-, andtriethanolamine; ethoxylated polysiloxanes and silicones; ethoxylatedthiols, including ethoxylated terdodecyl mercaptan; and ethoxylatedimidazoles.

To assist in incorporating the non-ionic surfactant in an aqueousmedium, the non-ionic surfactant can also include other components invarious proportions, including alcohols, refined crude oil fractions andpolar hydrocarbons. For example, isopropyl alcohol, naphthalene andheavy aromatic petroleum naphtha are useful for delivering the non-ionicsurfactant into an aqueous medium.

A commercially available non-ionic surfactant useful in an embodiment ofthe spacer fluid composition includes LoSurf-259™ Nonemulsifier(Halliburton Energy Services; Duncan, Okla.).

The non-ionic surfactant is present in the spacer fluid composition byvolume per barrel of base aqueous solution in the spacer fluidcomposition. The non-ionic surfactant is present in the spacer fluidcomposition in a range of from about 1.5 gallons to about 2.0 gallonsper barrel of base aqueous fluid. One of ordinary skill in the artrecognizes the appropriate amount of non-ionic surfactant for the spacerfluid composition given the application circumstances and thereforeunderstands that all values within the provided range are included.

Other Additives

The spacer fluid can include additional components, including, forexample, curing agents, salts, corrosion inhibitors, oxygen scavengers,scale inhibitors and formation conditioning agents. One of ordinaryskill in the art recognizes the appropriate amount and type of additivesfor a particular application.

Making Spacer Fluids

The spacer fluid composition forms by combining the viscosifier, theweighting agent, the antifoaming agent, and the non-ionic surfactantinto the base aqueous fluid. An example method of combining the spacerfluid components includes introducing into a vessel capable of retainingthe spacer fluid composition a sufficient quantity of base aqueousfluid. Introducing each component into the base aqueous fluid separatelyand mixing the blend such that all the spacer fluid components are fullyincorporated forms the spacer fluid composition. Blending means caninclude mixing using a low- or high-shear blender.

“On the fly” mixing of the components is not recommended because somecomponents are typically solids and the other components are typicallyliquids. Batch mixing of the spacer fluid components until homogeneousincorporation and formation of the space fluid composition is preferred.

Methods of Using the Spacer Fluid Composition

A method for using the spacer fluid composition includes using thespacer fluid to position one fluid into the well bore containing anotherfluid. In some cases, the two fluids are incompatible with one another.For instance, water-based cement slurries and oil-based drilling mudsare two fluids that are incompatible with one another. The spacer fluidused in the methods is compatible with both fluids. The well bore fluidinitially comprises only one fluid, such as the oil-based drilling mud.

As previously described, the well bore contains at least a portion of atubular, which has an internal fluid conduit and an external surface.The internal fluid conduit fluidly couples the surface with the wellbore. The well bore annulus forms between the external surface of thetubular and the well bore wall.

More than one fluid conduit coupling the surface with the well borepermits circulation of the well bore fluid. The well bore fluidcirculates from a first fluid conduit coupled with the surface throughthe well bore to a second fluid conduit coupled with the surface. Insome instances, the tubular is one of the fluid conduits and the wellbore fluid circulates through the internal fluid conduit of the tubular.The circulation rate of well bore fluid through the well bore isdeterminable in the well bore annulus.

When using the spacer fluid to displace one fluid with another, acertain amount of contamination occurs between fluids. At the interfaceof adjacent fluids, contamination occurs through direct contact at thefluid-fluid interface by way of diffusion. As fluids move, a minoramount of contamination occurs between the fluids. One fluid trailinganother fluid through a fluid system picks up remnants of the leadingfluid—off the well bore wall or from the surface of the tubular. Theamount of contamination in the trailing fluid increases with both timeand fluid flow rate.

In a method for using the spacer fluid, introduction and positioning ofeach fluid in the well bore occurs at a fluid flow rate that is laminaror in a “plug flow” regime. Contamination between the fluids is lower ifthe fluids remain in a stagnant position relative to one another. Asfluid flow increases—moving from laminar or plug flow towards aturbulent flow regime—the adjacent fluids begin physical mixing with oneanother as momentum acts on the fluids and pushes them into one another.Plug flow has an added benefit in practice of prolonging exposure of thewell bore wall and the exterior tubular wall to the surfactants and theaqueous base fluid in the spacer fluid.

Introduction of the spacer fluid occurs through the first fluid conduit.The first fluid conduit in some instances is the tubular, where thefluid passes through the internal fluid conduit into the well bore.Introduction of the spacer fluid occurs at a pressure sufficient toinduce laminar fluid circulation in the well bore fluid. Uponintroduction, the spacer fluid contacts the fluid in the well bore andcirculates the well bore fluid from the first fluid conduit to thesecond fluid conduit. The spacer fluid introduction displaces anequivalent amount of well bore fluid through the second fluid conduit.In some instances, the amount of spacer fluid displaces the entire wellbore. In other instances, the amount of spacer fluid displaces theannular space of the well bore. In yet some other instances, the amountof spacer fluid displaces the fluid present in the tubular internalfluid conduit. The spacer fluid while in the well bore becomes part ofthe well bore fluid.

Introduction of another fluid that is different from the well bore fluidinto the well bore occurs through the first fluid conduit. Introductionof another fluid into the well bore after the spacer fluid is at apressure sufficient to induce laminar fluid circulation in the well borefluid. When introduced, the post-spacer fluid contacts the spacer fluidin the well bore, causing the well bore fluid to circulate through thewell bore in a direction from the first fluid conduit to the secondfluid conduit. The second fluid introduction displaces an equivalentamount of well bore fluid through the second fluid conduit.

Positioning the second fluid occurs such that at least a portion of thefluid occupies at least some of the well bore annulus. In some methods,introduction of a third fluid to position the second fluid in the wellbore annulus using similar techniques as previously described withdisplaces well bore fluid. In most instances, the third fluid is anotheramount of spacer fluid, a spacer fluid with a different composition, orwater, including seawater and fresh water.

A method for using the spacer fluid includes fluidly isolating at leastpart of the well bore annulus in the well bore. The fluid used toisolate the well bore annulus is water-based cement slurry. In somemethods, the well bore contains an oil-based drilling fluid. Water-basedcement slurries and oil-based drilling fluids are incompatible. Thewater-based cement slurry cures into a solid cement material that iscapable of isolating at least part of the well bore annulus. The spacerfluid is compatible with both the oil-based drilling fluid and thewater-based cement slurry.

Introduction of the spacer fluid into the well bore occurs through afirst fluid conduit. The amount of spacer fluid introduced is at apressure adequate to induce laminar fluid circulation in the well borefluid such that it displaces an equivalent amount of well bore fluidthrough a second fluid conduit. The introduced spacer fluid contacts thewell bore fluid in the well bore.

Introduction of the water-based cement slurry occurs through the firstfluid conduit. The introduced water-based cement slurry induces laminarfluid circulation in the well bore fluid and displaces an equivalentamount of well bore fluid through the second fluid conduit. Thewater-based cement slurry contacts the spacer fluid portion of the wellbore fluid.

Positioning a portion of the water-based cement slurry in the well boreannulus occurs such that cement slurry contacts both the tubularexternal surface and the well bore wall. Maintaining the position of thewater-based cement permits the cement to adhere to the water-wetsurfaces of the well bore wall and tubular exterior. It also permits thewell bore conditions to induce curing in the cement. Upon curing, thewater-based cement slurry forms a solid cement material in the well boreannulus, fluidly isolating at least a portion of the well bore annulus.

In some methods, introduction of additional fluids into the well borethrough the first fluid conduit positions the water-based cement slurryin the well bore annulus. Introducing the additional fluid causes it tocontact the cement slurry while in the well bore. The additional fluidpartially displaces the well bore fluid such that the water-based cementslurry is in the well bore annulus.

The amount of spacer fluid employed in all methods is adequate to keepfluids separated, especially incompatible fluids during introduction andpositioning.

Examples of specific embodiments given facilitate a better understandingof the spacer fluid composition and method of use. In no way do theExamples limit or define the scope of the invention.

EXAMPLES

Mixing and testing of the Example spacer fluid compositions with thewater-based cements and oil-based muds both separately and incombination is in accordance with the procedure of Chapter 16 ofAmerican Petroleum Institute (API) Recommend Practice 10B-2 (2005),titled “Recommended Practice for Testing Well Cements”, which adoptsInternational Organization for Standardization (ISO) 10426-2.

Example Spacer Fluid Compositions 1-3

The procedures given in Section 16.2 of API RP 10B-2 guide thepreparation of the each example spacer fluid composition, water-basedcement slurry, and oil-based mud.

Example 1-3 spacer fluid compositions each incorporate an amount ofviscosifier (DIACEL® Adjustable Spacer Viscosifier), weighting agent(barite), antifoaming agent (DIACEL® ATF-S Antifoam) and non-ionicsurfactant (LOSURF™-259 Nonemulsifier) in an amount of base aqueousfluid (fresh water) per Table 1.

TABLE 1 Formulations for spacer fluid compositions Examples 1-3.Formulation of Spacer Examples 1-3 Weight- Non- Com- Fresh ing foamingNon-ionic Density ponents Water Viscosifier agent agent surfactant Lbm/Examples Bbls Lbs Lbs Gals Gals Ft{circumflex over ( )}3 Example 1 0.9276.8 108 0.1 1.5 77 Example 2 0.840 6.8 195 0.1 1.5 89 Example 3 0.7966.8 300 0.1 1.5 102

The water-based cement slurry Cement 1 for testing Example 1 is ClassG-based cement slurry having a density of 101 pounds-per-cubic foot(lb_(m)/ft³). The yield is 2.22 cubic feet of cement slurry from 11.36gallons of water per sack, based with 35% aggregate and othertraditional well bore cementing additives. Cement 2, used for testingExample 2, has the same formulation and properties as Cement 1. Thewater-based cement slurry Cement 3 for testing Example 3 is ClassG-based latex cement slurry having a density of 125 lb_(m)/ft³. Theyield is 1.37 cubic feet of cement slurry from 3.34 gallons of water persack, based with 35% aggregate and other traditional well bore latexcement additives.

The oil-based mud OBM 1 for testing Example 1 is a diesel oil-based mud(0.923 bbl diesel/bbl OBM) having a density of 56 pounds-per-cubic foot(lb_(m)/ft³). The oil-based mud OBM 2 for testing Example 2 is a safraoil-based (0.414 bbl/bbl OBM) mud having a density of 80 lb_(m)/ft³. Theoil-based mud OBM 3 for testing Example 3 safra oil-based (0.409 bbl/bblOBM) mud having a density of 81 lb_(m)/ft³.

Example 1

Table 2 shows the results of compatibility testing per Section 16.3 ofAPI RP 10B-2 (Rheology) for various mixtures of spacer fluid compositionExample 1, water-based cement slurry Cement 1 and oil-based mud OBM 1.The different volume ratios simulate different levels of contaminationand interaction between the various fluids downhole.

Viscosity trends at different blending ratios of two or more fluids andat different rotational viscosity rates help to demonstrate fluidcompatibility. Viscosity is a measure of the resistance of a fluid todeform under shear stress and the resistance of a material to flow. Asignificant viscosity increase indicates that the fluids areincompatible with one another, which would require greater head pressureto move the combined incompatible fluids through a fluid system.Likewise, a nonhomogeneous fluid admixture also indicates the fluids areincompatible. A chemical reaction may be one where solids suspended inone fluid flocculate out after the introduction of another fluid. If thetwo or more fluids mix and do not undergo undesirable chemical andphysical reactions then they are considered compatible with one another.

For measuring actual or true rotation viscosity, a rotational cylinderand bob instrument, for example a Fann viscometer, determines rotationalviscosity in centi-Poise (cP) at 300, 200, 100, 6 and 3rotations-per-minute (RPM). High viscosity readings across an entirerange of rotational viscosity readings indicate incompatibility betweenthe fluids in the mixture tested. A deviation from a linear trend inviscosity between two substances—such as a “bump” or “spike”—canindicate incompatibility at the compositional ratio tested.

Plastic Viscosity (PV), also measured in cP, is the resistance of afluid to continual flow, like kinetic friction. The Yield Point (YP),measured as pounds per 100 square feet, is the resistance of initialflow of fluid or the stress required in order to move the fluid, likestatic friction. Both PV and YP tend to increase with contamination ofan aqueous fluid. Water in an oil-based mud will increase the PV and YPvalues for the OBM.

TABLE 2 Compatibility tests between Example 1, OBM 1 and water-basedcement slurry Cement 1. Compatibility Testing of Example 1 PropertiesPlastic Yield Viscometer Readings Vis- Point 300 200 100 6 3 cosity lb/Fluid Mixtures cP cP cP cP cP cP 100 ft{circumflex over ( )}2 Cement 1 -101 PCF 17 13 9 3 2 12 5 Example 1 - 77 PCF 8 6 5 2 1 4 4 OBM 1 - 56 PCF15 12 9 5 4 9 6 OBM1:Ex1 95:5 17 14 11 7 6 9 9 OBM1:Ex1 75:25 21 17 13 76 12 10 OBM1:Ex1 50:50 25 20 14 7 6 16 9 OBM1:Ex1 25:75 9 7 5 2 1 6 3OBM1:Ex1 5:95 8 6 5 2 1 4 4 Cement1:Ex1 95:5 19 14 10 5 4 13 6Cement1:Ex1 75:25 15 11 8 4 3 10 5 Cement1:Ex1 50:50 16 12 8 4 3 12 4Cement1:Ex1 25:75 12 9 6 4 3 9 3 Cement1:Ex1 5:95 11 8 5 3 2 9 2OBM1:Cement1 95:5 16 13 11 7 6 7 9 OBM1:Cement1 30 24 17 9 8 19 11 75:25OBM1:Cennent1 38 30 23 13 12 22 16 50:50 OBM1:Cement1 25:75 31 25 17 1110 21 11 OBM1:Cement1 5:95 30 22 17 11 10 19 11 OBM1:Ex1:Cement1 15 12 94 3 9 6 25:50:25

The compatibility test results of Table 2 show favorable results spacerfluid composition Example 1 in all ratios with OBM 1 and Cement 1. Themixtures between OBM 1 and the water-based cement slurry Cement 1 revealincompatibility virtually across all blending ratios—viscosity profilenumbers greater than the viscosity profile values for OBM 1 and Cement 1base materials. Example 1 shows excellent compatibility at all ratioswith Cement 1. Example 1 has good compatibility with OBM 1, showing aminor viscosity “bump” occurring around the 75:25 and 50:50 OBM:spacerfluid ratio. The highest Yield Point for either the water-based cementslurry or the oil-based mud with the spacer fluid composition Example 1at any ratio is 10 lb_(m)/100 ft².

The 25:50:25 OBM1:Example1:Cement1 shows extremely good spacer fluidcompatibility during heavy contamination with both incompatible fluids.This demonstrates that Example 1 can maintain an easy-to-pump viscosityprofile even under heavy adjacent fluid contamination with both OBM 1and Cement 1 present. Comparatively, the viscosity profile of the 50:50OBM 1:Cement 1 mixture in Table 2 demonstrates a significantly higherviscosity profile.

One potential side effect of low-level contamination of the water-basedcement slurry is a shortening of its thickening time. The thickeningtime is the time in which it takes the water-based cement slurry toreach 100 Bearden units of consistency (BC), which is a dimensionlessvalue. At values higher than 100 Bearden units, cement slurries are notpumpable.

Table 3 shows the results of modification to cement slurry thickeningtime per Section 16.4 of API RP 10B-2 for uncontaminated Cement 1 andmixtures of Example 1 and Cement 1.

TABLE 3 Thickening Time test results for Cement 1 and Cement 1:Example 1mixtures. Thickening Time Tests for Cement 1 with Example 1 PropertiesThickening Time Bearden Reading Units Fluid Mixtures Minutes BC Cement1310 100 Cement1:Ex1 95:5 430 100 Cement1:Ex1 75:25 480 12

The results in Table 3 show that thickening time increases withcontamination of Cement 1 with amounts of Example 1. The resultsindicate that a minor amount of Example 1 contamination into Cement 1does not cause Cement 1 to set up prematurely and become unpumpable.

The compressive strength of the uncontaminated cement and spacer fluidcontaminated admixtures are in Table 4. The compressive strength testsuse an ultrasonic cement analyzer. The procedures of Clause 8(Non-destructive Sonic Testing of Cement) as well as Chapter 16.5 of APIRP 10B-2 guide the preparation and testing of the water-based cementslurry and the admixtures using the ultrasonic cement analyzer.

TABLE 4 Sonic Compressive Strength Tests between Cement 1 and Cement1:Example 1 mixtures. Sonic Compressive Strength Tests for Cement withExample 1 Properties Compressive Strength @ 24 Time to 50 Psi Time to500 Psi hours Fluid Mixtures Minutes Minutes Psi Cement1 416 728 888Cement1:Ex1 95:5 456 916 705 Cement1:Ex1 75:25 1380 +1440 67

The results in Table 4 confirm a lengthening of the time to harden intosolid cement suggested by the results given in Table 3.

Table 5 shows the results of modification to cement slurry fluid lossper Clause 10 and Section 16.6 of API RP 10B-2 for uncontaminated Cement1 and mixtures of Example 1 and Cement 1.

TABLE 5 Fluid Loss Tests between Cement 1 and Cement 1:Example 1mixtures. Fluid Loss Tests for Cement with Example 1 Properties FluidLoss @ 30 Minutes Fluid Mixtures Cm 3 Cement1 146 Cement1:Ex1 95:5 322Cement1:Ex1 75:25 248

Table 5 shows improvement in fluid loss for the Cement 1:Example 1mixtures versus the uncontaminated Cement 1.

Example 2

Table 6 shows the results of compatibility testing per Section 16.3 ofAPI RP 10B-2 (Rheology) for various mixtures of spacer fluid compositionExample 2, water-based cement slurry Cement 2 and oil-based mud OBM 2.

TABLE 6 Compatibility tests between Example 2, OBM 2 and water-basedcement slurry Cement 2. Compatibility Testing of Example 2 PropertiesPlastic Yield Viscometer Readings Vis- Point 300 200 100 6 3 cosity lb/Fluid Mixtures cP cP cP cP cP cP 100 ft{circumflex over ( )}2 Cement 2 -101 PCF 17 13 9 3 2 12 5 Example 2 - 89 PCF 11 8 6 3 2 7 4 OBM 2 - 80PCF 26 22 16 8 6 15 12 OBM2:Ex2 95:5 70 57 41 18 6 43 29 OBM2:Ex2 75:25120 97 70 27 23 75 49 OBM2:Ex2 50:50 26 16 11 6 4 22 3 OBM2:Ex2 25:75 107 5 3 2 7 2 OBM2:Ex2 5:95 9 7 5 3 2 6 3 Cement2:Ex2 95:5 17 14 9 4 3 126 Cement2:Ex2 75:25 16 14 10 9 6 9 8 Cement2:Ex2 50:50 15 13 9 7 6 9 7Cement2:Ex2 25:75 13 10 7 4 3 9 4 Cement2:Ex2 5:95 12 10 7 4 3 7 5OBM2:Cement2 95:5 53 44 33 15 14 30 25 OBM2:Cement2 75:25 46 33 24 11 1433 13 OBM2:Cement2 50:50 62 37 23 9 8 58 1 OBM2:Cement2 25:75 46 33 2411 9 33 13 OBM2:Cement2 5:95 27 20 13 6 5 21 6 OBM2:Ex2:Cement2 17 13 94 3 12 5 25:50:25

The compatibility test results of Table 6 show favorable results spacerfluid composition Example 2 in all ratios with OBM 2 and Cement 2. Themixtures between OBM 2 and the water-based cement slurry Cement 2 revealincompatibility virtually across all blending ratios—viscosity profilenumbers greater than the viscosity profile values for OBM 2 and Cement 2base materials. Example 2 shows excellent compatibility at all ratioswith Cement 2. Example 2 is generally compatible with OBM 2, althoughthe viscosity “bump” for the 95:5 and 75:25 OBM:spacer fluid ratio isconsidered somewhat elevated. The highest Yield Point is 49 lb_(m)/100ft².

The 25:50:25 OBM 2:Example 2:Cement 2 shows extremely good spacer fluidcompatibility during heavy contamination with both incompatible fluids.Comparatively, the viscosity profile of the 50:50 OBM 2:Cement 2 mixturein Table 6 demonstrates a significantly higher viscosity profile.

Example 3

Table 7 shows the results of compatibility testing per Section 16.3 ofAPI RP 10B-2 (Rheology) for various mixtures of spacer fluid compositionExample 3, water-based cement slurry Cement 3 and oil-based mud OBM 3.

TABLE 7 Compatibility tests between Example 3, OBM 3 and water-basedcement slurry Cement 3. Compatibility Testing of Example 3 with OBM andCement Properties Viscometer Readings 300 200 100 6 3 Plastic ViscosityYield Point Fluid Mixtures cP cP cP cP cP cP lb/100 ft{circumflex over( )}2 Cement 3 - 125 PCF 151 103 50 19 15 151 0 Example 3 - 102 PCF 1511 7 3 2 12 3 OBM 3 - 81 PCF 56 45 34 17 16 33 25 OBM3:Ex3 95:5 79 63 4521 19 51 30 OBM3:Ex3 75:25 139 102 66 26 24 109 31 OBM3:Ex3 50:50 29 2013 7 6 24 5 OBM3:Ex3 25:75 12 10 6 3 2 9 4 OBM3:Ex3 5:95 17 13 9 3 2 125 Cement3:Ex3 95:5 128 89 51 11 9 115 13 Cement3:Ex3 75:25 49 34 22 8 640 9 Cement3:Ex3 50:50 34 29 17 5 3 33 7 Cement3:Ex3 25:75 40 32 24 1513 24 17 Cement3:Ex3 5:95 18 14 11 6 3 10 8 OBM3:Cement3 95:5 90 74 5424 22 54 39 OBM3:Cement3 75:25 +300 240 159 44 35 ND ND OBM3:Cement350:50 +300 +300 +300 220 160 ND ND OBM3:Cement3 25:75 154 131 93 22 1791 69 OBM3:Cement3 5:95 141 100 61 17 14 120 22 OBM3:Ex3:Cement3 29 2314 5 4 22 7 25:50:25

The compatibility test results of Table 7 show favorable results spacerfluid composition Example 3 in all ratios with OBM 3 and Cement 3. Themixtures between OBM 3 and the water-based cement slurry Cement 3 revealsignificant incompatibility virtually across all blending ratios. Thelatex/water based cement slurry and the OBM are virtually immobile atall mixture ratios. Example 3 shows excellent compatibility at allratios with Cement 3. Example 3 is generally compatible with OBM 3,although the viscosity “bump” for the 95:5 and 75:25 OBM:spacer fluidratio is considered somewhat elevated. The highest Yield Point is 31lb_(m)/100 ft².

The 25:50:25 OBM 2:Example 2:Cement 2 shows excellent spacer fluidcompatibility during heavy contamination with both incompatible fluids.Comparatively, the viscosity profile of the 50:50 OBM 3:Cement 3 mixturein Table 7 demonstrates appears virtually unpumpable.

Table 8 shows the results of modification to cement slurry thickeningtime per Section 16.4 of API RP 10B-2 for uncontaminated Cement 3 andmixtures of Example 3 and Cement 3.

TABLE 8 Thickening Time test results for Cement 3 and Cement 3:Example 3mixtures. Thickening Time Tests for Cement with Example 3 PropertiesThickening Bearden Time Reading Units Fluid Mixtures Minutes BC Cement 3341 100 Cement3:Ex3 95:5 390 100 Cement3:Ex3 75:25 390 14

The results in Table 3 show that with a minor amount of contamination(95:5 cement slurry/spacer fluid) that the time to reach an equivalentBearden units as the uncontaminated slurry is approximately 14% longer.

The compressive strength of the uncontaminated cement and spacer fluidcontaminated admixtures are in Table 9. The compressive strength testsuse an ultrasonic cement analyzer. The procedures of Clause 8(Non-destructive Sonic Testing of Cement) as well as Chapter 16.5 of APIRP 10B-2 guide the preparation and testing of the water-based cementslurry and the admixtures using the ultrasonic cement analyzer.

TABLE 9 Sonic Compressive Strength Tests between Cement 3 and Cement3:Example 3 mixtures. Sonic Compressive Strength Tests for Cement withExample 3 Properties Compressive Strength @ 24 Time to 50 psi Time to500 psi hours Fluid Mixtures Minutes Minutes Psi Cement 3 385 421 2393Cement3:Ex3 95:5 319 365 2969 Cement3:Ex3 75:25 476 515 1056

The results in Table 9 show that a minor amount of contamination (95:5Cement 3:Example 3) causes the cement slurry to harden into a solidcement that is approximately 25% stronger than the uncontaminated Cement3. The minor amount of contamination of spacer fluid Example 3 in cementslurry Cement 3 also causes the cement slurry to reach the 50 and 500psi strength measuring points 18% and 12% faster than uncontaminatedcement, respectively.

Table 10 shows the results of modification to cement slurry fluid lossper Clause 10 and Section 16.6 of API RP 10B-2 for uncontaminated Cement3 and mixtures of Example 3 and Cement 3.

TABLE 10 Fluid Loss Tests between Cement 3 and Cement 3:Example 3mixtures. Fluid Loss Tests for Cement with Example 3 Properties FluidLoss @ 30 Minutes Fluid Mixtures Cm 3 Cement 65 Cement:Ex. 3 95:5 46Cement:Ex. 3 75:25 69

As with the other compatibility tests, the slightly contaminated Cement1:Example 1 (95:5) mixture shows better performance than uncontaminatedCement 3 through about 30% reduction in fluid loss after 30 minutes. Theresults in Table 10 show good compatibility between Example 3 spacerfluid and Cement 3 and, in fact, improved performance in the presence ofa minor amount of Example 3 spacer fluid.

What is claimed is:
 1. A spacer fluid composition for use between afirst fluid and a second fluid, the spacer fluid composition comprising:a base aqueous fluid comprising fresh water, a viscosifier comprising achemically modified tannin, a weighting agent comprising barite, anantifoaming agent comprising a silicone-based liquid, and a non-ionicsurfactant comprising an alkoxylated alcohol, where a measured viscosityof a mixture of the first fluid and the spacer fluid composition at afirst ratio of the first fluid to the spacer fluid composition is lessthan a measured viscosity of a mixture of the second fluid and the firstfluid at a second ratio of the second fluid to the first fluid, wherethe first ratio and second ratio are substantially the same, and wherethe second fluid comprises an oil-based fluid and the first fluidcomprises a water-based cement slurry, where a measured viscosity of amixture of the second fluid and the spacer fluid composition at a thirdratio of the second fluid to the spacer fluid composition is less than ameasured viscosity of a mixture of the second fluid and the first fluidat the second ratio of the second fluid to the first fluid, where thethird ratio is substantially the same as the first ratio and the secondratio, where a measured viscosity of the spacer fluid composition isless than a measured viscosity of the first fluid and a measuredviscosity of the second fluid, and where the spacer fluid compositionmaintains compatibility with both the first fluid and the second fluidduring heavy contamination when the volume percent of the spacer fluidcomposition is about 50% by volume in a mixture comprising the spacerfluid composition, the first fluid at about 25% by volume, and thesecond fluid at about 25% by volume, and where the first fluid isoperable to mix with the spacer fluid composition up to a volume ratioof about 95:5 first fluid to spacer fluid composition, such that thewater-based cement slurry compressive strength upon setting to a solidcement is increased by at least about 25% at about 24 hours compared tothe water-based cement slurry alone.
 2. The spacer fluid composition ofclaim 1 where the first fluid and the second fluid are incompatible, anddo not readily mix with one another.
 3. The spacer fluid composition ofclaim 1 where the water-based cement slurry is a water-based latexcement slurry.
 4. The spacer fluid composition of claim 1 where thespacer fluid composition is operable to produce a 75:25 volume percentmixture of spacer fluid composition to an oil-based drilling mud havinga yield point value of no greater than about 49 pounds per 100 squarefeet.
 5. The spacer fluid composition of claim 1 where the chemicallymodified tannin is a sulfomethylated tannin.
 6. The spacer fluidcomposition of claim 1 where the viscosifier is in a range of from about5 pounds to about 10 pounds per barrel of base aqueous fluid present inthe spacer fluid composition.
 7. The spacer fluid composition of claim 1where the weighting agent is in a range of from about 100 pounds toabout 400 pounds per barrel of base aqueous fluid in the spacer fluidcomposition.
 8. The spacer fluid composition of claim 1 where thedensity of the spacer fluid is in a range of from about 70 to about 120pounds per cubic foot.
 9. The spacer fluid composition of claim 1 wherethe alkoxylated alcohol is an ethoxylated alcohol.
 10. The spacer fluidcomposition of claim 1 where the antifoaming agent is in a range of fromabout 0.01 gallons to about 0.2 gallons per barrel of base aqueous fluidin the spacer fluid composition.
 11. The spacer fluid composition ofclaim 1 where the non-ionic surfactant agent is in a range of from about1.5 gallons to about 2.0 gallons per barrel of base aqueous fluid in thespacer fluid composition.
 12. The spacer fluid composition of claim 1where the non-ionic surfactant further comprises isopropyl alcohol,naphthalene and heavy aromatic petroleum naphtha.
 13. The spacer fluidcomposition of claim 1, where the water-based cement slurry has adensity in a range of from about 101 pounds per cubic foot to about 125pounds per cubic foot.
 14. The spacer fluid composition of claim 1,where the oil-based fluid has a density in a range of from about 56pounds per cubic foot to about 81 pounds per cubic foot.
 15. The spacerfluid composition of claim 1, where the chemically modified tannin is ata concentration of about 8.5 pounds per barrel, the barite is at aconcentration of about 377 pounds per barrel, the silicone liquid is ata concentration of about 0.1 gallons per barrel, and the alkoxylatedalcohol comprises an ethoxylated alcohol at a concentration of about 1.9pounds per barrel.